Television (TV) networks have traditionally utilized analog signal formats to carry video and audio channels to television viewers or subscribers. All the television signals may each be modulated at a different radio frequency (RF) and combined or multiplexed for transmission over the terrestrial air or a hybrid fiber-coaxial cable network. The customer premise equipment (CPE), such as a TV set or cable set-top box converter, receives all such signals combined, and tunes to a particular frequency in order to display the TV channel desired by the viewer.
With various advancements in digital communications and the introduction of digital television (DTV), TV network providers have been replacing or otherwise upgrading their transmission and distribution systems to provide new and/or better quality services to their viewers or paid subscribers. In addition to transmitting analog signals, the infrastructure of these upgraded or new systems are also adapted to facilitate the generation and transmission of various digital formats that provide superior picture and sound quality, higher channel capacity, high-speed Internet data services, voice services and/or interactive services. Given the size of existing television infrastructure, television network providers must also provide support for legacy systems, and therefore, provide support for both analog and digital television systems.
Since a plurality of analog and/or digital channels are multiplexed onto and transmitted by the TV network provider infrastructure, the CPE may have the capability to determine whether a channel may comprise an analog or digital signal and also determine the modulation and/or coding scheme used. In the absence of a quick way to determine the signal format, the CPE may have to try to demodulate and decode every possible modulation and coding scheme which may be time consuming.
Current analog TV signals are defined primarily by the National Television Standards Committee (NTSC), the Phase Alternative Line (PAL) or the Sequential Couleur Avec Memoire (SECAM) systems, and used in different countries around the world. An analog TV signal utilizes at least two RF carriers, combined in the same channel band. In this regard, a first carrier may commonly be amplitude modulated (AM) with video content, while one or more other carriers may be frequency modulated (FM), amplitude modulated (AM), or quaternary phase-shift keyed (QPSK) with audio content. An analog TV receiver functions by performing a series of operations comprising adjusting the signal power, separating the video and audio carriers, and demodulating each carrier in order to down-convert the signals to baseband. The baseband video signal may then be decoded and displayed by achieving horizontal and vertical synchronization and extracting the luminance and color information. After demodulating the received signal, the resulting baseband audio may be decoded, and left, right, surround channels and/or other information may be extracted.
Current digital TV signals utilize a plurality of modulation techniques for transmitting and receiving packetized information comprising one or more digitized and compressed TV programs, Internet data and/or voice data. Current digital TV standards in the U.S. define the use of quadrature amplitude modulation (QAM) of different levels including quaternary phase shift keying (QPSK), 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, 512-QAM, and 1024-QAM for digital cable transmission. Additionally, current digital TV standards in the U.S. define the use of vestigial sideband (VSB) modulation including 2-VSB, 4-VSB, 8-VSB, 16-VSB for terrestrial digital transmission among other schemes. Similarly, DVB and ISDB are other standards used for cable and terrestrial digital transmission in various countries around the world. A QAM or VSB receiver functions by performing a series of operations comprising adjusting the signal power, locking to the carrier, and down-converting to baseband. The baseband digital signal may be demodulated by trying a series of schemes, and processing may include error correction and decompression to reproduce the picture and sound, or processed as internet or voice data.
In a conventional TV CPE, after tuning to a channel frequency, the TV set or set-top box normally detects whether or not a channel comprises an analog or digital signal, or any signal at all, by performing the all of receive functions outlined above. If the receiver successfully creates and validates a bit stream from the RF carrier using a QAM scheme, for example, then a QAM signal has been detected. If the receiver successfully creates and validates a bit stream from the RF carrier using a VSB scheme, for example, then a VSB signal has been detected. If a receiver successfully locks to the video and audio carriers of an analog signal, then an analog, NTSC for example, TV signal has been detected. Otherwise the receiver found no signal at all.
One example of problems presented by slow detection of TV signals is when a receiver is connected to a cable or over-the-air terrestrial network and performs a scan of the television channels to detect and possibly store the type of signal present on each channel. Slow detection of the signal on a TV channel is increasingly problematic as advances in digital communications and introduction of digital television have led to an increasing number of television channels and thus an increasing amount of time required to complete a scan of the channels.
In a cable modem used for receiving Internet data, the cable modem receiver must detect only digital QAM signals. When a cable modem has to wait until a valid bit stream is created for each detection attempt, the usual latency associated with a connection increases. Furthermore, the latency due to the waiting process is further exacerbated when the modem has to scan all the available RF channels in order to detect which RF channel comprises the appropriate Internet information.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.